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Alex Nold, Jared Dicioco, Alec Sequeira, Colin Fox, Dominic Globa 22.1 The Nature of Species and the Biological Species Concept Sympathetic species inhabit the same locale but remain distant. Populations of a species exhibit geographic variation. The biological species concept focuses on the ability to exchange genes. Prezygotic isolating mechanisms prevent the formation of a zygote. Postzygotic isolating mechanisms prevent normal development into reproducing adults. The biological species concept does not explain all observations. 22.2 Natural Selection and Reproductive Isolation Among the factors that separate populations and species are geographical ecological behavioral temporal and mechanical isolation as well as factors that inhibit fusion of gametes are the normal development of the hybrid organisms. Some isolating mechanisms prezygotic prevent hybrid formation others postzygotic prevent hybrids from surviving and reproducing. 22.3 The Role of Genetic Drift and Natural Selection in Speciation In small populations, genetic drift may cause populations to diverge; the differences that evolve may cause the populations to become reproductively isolated. Adaptation can lead to speciation: adaptation to different situations or environments may incidentally lead to reproductive isolation. In contrast to reinforcement these differences are not directly favored by natural selection because they prevent hybridization. Natural selection can directly select for traits that increase reproductive isolation. 22.4 The Geography of Speciation Speciation is a two-part process 1. Initially identical populations must diverge 2. Reproductive Isolation must occur to preserve these differences Allopatric (geographically separated) populations appear much more likely to have substantial differences leading\to speciation Polyploidy- produces individuals that have more than two sets of chromosomes Autopolyploidy- all chromosomes derive from a single species Allopolyploidy- happens when two species hybridize 22.5 Adaptive Radiation and Biological Diversity -Adaptive radiation occurs when a species finds itself in a new or suddenly changed environment with many resources and few competing species. -One example of adaptive radiation is the Galapagos islands -Adaptive radiation can also result when key innovation evolves within a species allowing it to use previously inaccessible resources 1 http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0073532223/8113 33/Stimulation_of_Genetic_Drift.swf::Simulation%20of%20Genetic%20Drift 1 2 3 4 True or False. Geographical is a factor to populations and animal species. True or False. Habituation is a factor to populations and species. True or False. Mechanical Isolation is a factor to populations and species. True or False. Ecological and behavioral are not factors to populations and species. 5 6 7 8 True or False. Temporal is a factor to populations and species. What prevents hybrids? a a.Prezygotic b b.Postzygotic c c.Gyzotic d d.a and b only